Uplink Control Signaling in Cellular Telecommunication System

ABSTRACT

A method, apparatus, and computer program for controlling allocation of control message fields in uplink transmission in a cellular telecommunication system are presented. Uplink control message fields are allocated to the resources of a physical uplink shared traffic channel according to an uplink transmission scheme selected for a user terminal. The control message fields are allocated so that transmission performance of the control messages is optimized for the selected uplink transmission scheme.

FIELD

The invention relates to the field of cellular radio telecommunicationsand, particularly, to uplink signaling.

BACKGROUND

A communication system known as an evolved UMTS (Universal MobileTelecommunication System) terrestrial radio access network (E-UTRAN,also referred to as UTRAN-LTE for its long-term evolution or LTE-A forlong-term evolution—Advanced) is currently under development within the3GPP. In this system, the downlink radio access technique will be OFDMA(Orthogonal Frequency Division Multiple Access), and the uplink radioaccess technique will be Single-Carrier FDMA (SC-FDMA) which is a typeof a linearly pre-coded OFDMA. The uplink system band has a structurewhere a Physical Uplink Control Channel (PUCCH) is used for transferringuplink control messages, and a Physical Uplink Shared Channel (PUSCH) isused for transmission of uplink user traffic. Additional controlmessages may be transmitted in resources initially allocated to thePUSCH. The PUCCH carries uplink control information, such as ACK/NACKmessages, channel quality indicators (CQI), scheduling requestindicators (SRI), channel rank indicators, downlink pre-codinginformation, etc.

BRIEF DESCRIPTION

According to an aspect of the present invention, there is provided amethod as specified in claim 1.

According to another aspect of the present invention, there is providedan apparatus as specified in claim 14.

According to another aspect of the present invention, there is provideda base station of a cellular telecommunication system as defined inclaim 26.

According to another aspect of the present invention, there is provideda user terminal of a cellular telecommunication system as defined inclaim 27.

According to another aspect of the present invention, there is providedan apparatus as specified in claim 28.

According to yet another aspect of the present invention, there isprovided a computer program product embodied on a computer readabledistribution medium as specified in claim 29.

Embodiments of the invention are defined in the dependent claims.

LIST OF DRAWINGS

Embodiments of the present invention are described below, by way ofexample only, with reference to the accompanying drawings, in which

FIG. 1A illustrates a principle of cellular communications;

FIG. 1B illustrates an uplink system band structure in a modern UMTSsystem;

FIG. 2 illustrates transmitter and receiver structures for use in thecellular communications;

FIG. 3 illustrates current uplink signal structures in modern UMTS;

FIG. 4 is a flow diagram illustrating a process for carrying controlmessage field allocation according to an embodiment of the invention;

FIGS. 5A and 5B illustrate effects of the control message fieldallocation according to an embodiment of the invention;

FIG. 6A illustrates a detailed process for control message fieldallocation according to an embodiment of the invention;

FIG. 6B illustrates the effect of the control message field allocationaccording to FIG. 6A; and

FIG. 7 illustrates multi-stream transmission according to an embodimentof the invention.

DESCRIPTION OF EMBODIMENTS

The following embodiments are exemplary. Although the specification mayrefer to “an”, “one”, or “some” embodiment(s) in several locations, thisdoes not necessarily mean that each such reference is to the sameembodiment(s), or that the feature only applies to a single embodiment.Single features of different embodiments may also be combined to provideother embodiments.

A general architecture of a cellular telecommunication system providingvoice and data transfer services to mobile terminals is illustrated inFIGS. 1A and 1B. FIG. 1A illustrates a generic scenario of cellularcommunications where a base station 100 provides user terminals 110 to122 with wireless communication services within a cell 102. The basestation 100 may belong to a radio access network of a long-termevolution (LTE) or LTE-advanced (LTE-A) of the UMTS (Universal MobileTelecommunication System) specified within 3GPP (3^(rd) GenerationPartnership Project) and, therefore, support at least OFDMA and SC-FDMAas radio access schemes for downlink and uplink, respectively. The basestation is connected to other parts of the cellular telecommunicationsystem, such as a mobility management entity (MME) controlling mobilityof the user terminals, one or more gateway nodes through which data isrouted, and an operation and maintenance server configured to controlcertain communication parameters, as is known in the art.

FIG. 1B illustrates a generic structure of an uplink system bandallocated to a network operator for providing uplink communicationservices according to LTE Releases 8 and 9. The system band isstructured such that a traffic channel, i.e. a physical uplink sharedchannel (PUSCH), is allocated in the middle of the system band and acontrol channel, i.e. a physical uplink control channel (PUCCH), isallocated to both edges of the traffic channel band. The size of thePUCCH band is configurable by the base station 100, and in certainnetwork deployments the base station 100 may configure the utilizationof the band such that the frequency resources at the edges of the systemband are left blank. In current scenarios of the LTE system, uplinkL1/L2 control signaling is divided into two classes in the LTE system:control signaling in the absence of UL data, which takes place on thePUCCH, and control signaling in the presence of UL data, which takesplace on the PUSCH. PUCCH is a shared frequency/time resource reservedexclusively for user terminals transmitting only L1/L2 control signals.This description focuses on the PUSCH control signaling, wherein thePUSCH carries the uplink L1/L2 control signals in the case when the UEhas been scheduled for data transmission.

FIG. 2 illustrates very basic structures of an SC-FDMA transmitter(blocks 200 to 212) and an SC-FDMA receiver (blocks 214 to 226). It hasbeen envisaged that future Releases of the LTE system utilize OFDM inuplink direction as well. The structure is well known to a personskilled in the field of modern telecommunication systems, so FIG. 2 willbe described on a general level. In the SC-FDMA transmitter, modulatedsymbols to be transmitted are first transferred from a serial toparallel form in block 200, and transformed into a frequency domainthrough discrete Fourier transform (DFT) in block 202. Control andtraffic data symbols are allocated to corresponding frequency resourceelements in a resource element mapping block 204 according to adetermined criterion. The resource element may be a sub-carrier or avirtual sub-carrier, which is the term widely used in the context ofSC-FDMA transmission. Then, inverse DFT is calculated in block 206, thesignal is converted from the parallel to serial form in block 208, acyclic prefix is added in block 210, and the signal is transformed intoan analog form and transmitted through radio frequency (RF) parts of thetransmitter in block 212. In the receiver, the radio signal is receivedthrough an antenna and RF parts of the receiver in block 214 and thereceived signal is transformed into a digital domain. The cyclic prefixis removed in block 216, and serial-to-parallel conversion is performedin block 218 before DFT in block 220. The control and traffic datasymbols are extracted from their resource elements in block 222 beforethe inverse DFT in block 224 and parallel-to-serial conversion in block226.

It has been envisaged that the future LTE versions will support OFDMalso in the uplink. For such a case, it is simple to modify the SC-FDMAtransmitter and receiver structure to simply short-circuit DFT block 202in the transmitter and inverse DFT block in the receiver to provide anOFDM transmitter and receiver. Accordingly, the transmitter may comprisea controller controlling short-circuiting of the DFT block 202, and thereceiver may comprise a corresponding controller controllingshort-circuiting of the inverse DFT block 224. Additionally, future userterminals will be equipped with capability to support single-usermultiple-input-multiple-output transmission (SU-MIMO) in uplink, whereinthe uplink transmission is multiplexed spatially to achieve higher datarates and better spectral efficiency. For that purpose, the transmitterand receiver structures of FIG. 2 will be modified to include one signalbranch (FIG. 2 illustrates one branch) for each transmission/receptionantenna and a signal processor carrying out signal processing accordingto the selected multi-antenna transmission scheme. The signal processormay be located practically at any location in the digital domain of thetransmission/reception chain, which is obvious to one skilled in theart. The SU-MIMO transmission may be utilized together with either OFDMor SC-FDMA transmission.

For the sake of notation and to discriminate coded symbols mapped toeach resource element from OFDM or SC-FDMA symbols carrying a pluralityof coded symbols, both OFDM and SC-FDMA symbols can be seen as symbolblocks carrying a plurality of (modulated and channel-coded) symbols asinformation elements.

FIG. 3 illustrates a current uplink PUSCH sub-frame structure andallocation of control message fields to the PUSCH resources, i.e. afrequency resource block allocated to a given user terminal in a casewhen a cyclic prefix having a normal length is assumed. A time slotincludes seven SC-FDMA symbols, and the sub-frame comprises two timeslots. With an extended cyclic prefix, a time slot includes six SC-FDMAsymbols. The actual mix of different L1/L2 control signals and theirsize vary from sub-frame to sub-frame. Both the user terminal and thebase station have the knowledge about the number of symbols reserved bythe control part, as will be described later. A reference signal (RS) istransmitted on every sub-carrier of the centermost symbol of a timeslot. An acknowledgment message (ACK/NACK) indicating correct (ACK) orerroneous (NACK) reception of a downlink data packet is located onSC-FDMA symbols next to that conveying the RS so as to improve thereception quality of important ACK/NACK messages. The resource elementsallocated to the ACK/NACK message are located at one end of the SC-FDMAsymbol. A rank indicator indicating downlink channel rank may beallocated to the same sub-carriers as the ACK/NACK but on SC-FDMAsymbols adjacent to those of the ACK/NAK. There are at maximum twoSC-FDMA symbols per slot allocated to ACK/NACK signaling per (virtual)subcarrier. The same applies to the Rank Indicator. A channel qualityindicator (CQI) message field is allocated to the other end of theresource elements, and it may be transmitted using multiple SC-FDMAsymbols.

At this stage it is noted that the term ‘sub-carrier’ refers tosub-carriers operated in block 204, while the term may not be mostappropriate in the sense that the transmitted radio signal does not havethe form of a multi-carrier signal. Therefore, the term “virtualsub-carrier” has also been used in the context of SC-FDMA transmission.

The structure illustrated in FIG. 3 is suitable for SC-FDMAtransmission, because the DFT operation effectively spreads the contentsof each sub-carrier over the frequency domain. However, in OFDMtransmission the DFT operation is omitted and, as a consequence, thestructure of FIG. 3 becomes sub-optimal due to the fixed and localizedlocations of the control message fields. In practice, this means thatthe sub-carriers are not spread over the frequency resource block andbecome susceptible to frequency-selective fading. If the frequencies ofthe sub-carriers carrying ACK/NACK messages attenuate heavily because ofthe fading, the whole ACK/NACK message is likely to be lost.Additionally, or alternatively, the SU-MIMO transmission scheme shouldbe utilized effectively to improve the transmission performance of vitalcontrol messages in the uplink transmission.

FIG. 4 is a flow diagram illustrating a process for utilizing PUSCHresources for transmitting control messages according to an embodimentof the invention. The process may be carried out in the transmitter orthe receiver, i.e. in the user terminal or in the base station, as willbe described in greater detail below. The process starts in block 400.In block 402, an uplink transmission scheme is selected for the userterminal. In block 404, PUSCH resources are determined for the userterminal. In block 406, control message fields are allocated to thePUSCH resources determined in block 404 according to the transmissionscheme selected in block 402.

The selection of the transmission scheme may comprise selection betweenOFDM and SC-FDMA transmission and between single-stream and multi-streamtransmission. The selection may be carried out through selection of achannel rank which may automatically define the multi-antennatransmission method and the multiple access scheme (or uplink waveform).The selection of the uplink transmission scheme may be carried out bythe base station, and the transmission scheme may be signaled to theuser terminal in downlink signaling. The selection between thesingle-antenna and multi-antenna transmission scheme may be based on thechannel rank indicator transmitted from the user terminal. The channelrank indicates the number of available spatial MIMO channels.Accordingly, block 402 includes selection of the uplink transmissionscheme and indication of the transmission scheme to the user terminalwhen the process is executed in the base station. Similarly, block 404includes scheduling of uplink PUSCH resources to the user terminal,signaling the allocated PUSCH resources to the user terminal, andconfiguring a receiver of the base station to receive the uplinktransmission of the user terminal from the allocated PUSCH resources.Block 406 includes determining a pattern for data and control messagefields in the allocated PUSCH resources and configuring the receiver toreceive the data and the control messages accordingly.

When executed in the user terminal, block 402 includes deduction of theuplink transmission scheme from a control message received from the basestation, block 404 includes deduction of the uplink PUSCH resourcesallocated to the user terminal from a control message received from thebase station, and block 406 includes determining a pattern for the dataand control message fields in the allocated PUSCH resources andconfiguring the transmitter to transmit the data and the controlmessages accordingly.

When the selected uplink transmission scheme is SC-FDMA, the controlmessage fields may be allocated in a conventional manner, as illustratedin FIG. 3. In other words, the sub-carrier mapping of control messagefields may be carried out such that the control message fields arelocalized with respect to the allocated PUSCH resource. The DFT thenspreads the sub-carriers over the allocated frequency resource. On theother hand, when the selected uplink transmission scheme is OFDM,symbols of each control message field are distributed over the PUSCHfrequency resources of the user terminal. Accordingly, each controlmessage field becomes distributed along the frequency spectrum allocatedto the user terminal, which results in better tolerance againstfrequency-selective fading compared with using the structure of FIG. 3with OFDM transmission.

The transmission scheme is typically selected by the base station. Thebase station may first select the applied multi-antenna transmissionscheme: spatial multiplexing through a plurality of spatially paralleltransmission streams or beamforming or transmit diversity transmissionthrough a single stream (single-input-multiple-output, SIMO). Theselection may be made on the basis of the uplink channel rank, i.e. thenumber of uncorrelated uplink spatial sub-channels. When the basestation selects the spatial multiplexing as a multi-antenna transmissionscheme, the base station also selects the number of spatially paralleluplink sub-streams. Then, the selection between the OFDM and SC-FDMA maybe made on the basis of the selected multi-antenna transmission scheme:OFDM for spatial multiplexing and SC-FDMA for single-stream beamformingor SIMO. However, embodiments of the invention described below are notlimited to this type of selection of the transmission scheme, andSC-FDMA (or OFDM) may be used for all multi-antenna transmissionschemes. The transmission scheme (multi-antenna scheme and multi-accessscheme) may be determined in the user terminal by dynamic schedulinggrants, e.g. downlink control information (DCI) Format 0), signaled fromthe base station to the user terminal in downlink signaling. Thesignaling may be carried out explicitly by using at least one signalingbit indicating whether or not to use spatial multiplexing. Then, theuser terminal implements either spatial multiplexing with OFDM orbeamforming with SC-FDMA. Alternatively, the base station may signal thetransmission scheme implicitly by transmitting an uplink rank indicator.If the rank indicator indicates a channel rank higher than one, the userterminal implements either spatial multiplexing with OFDM. Otherwise,the user terminal implements beamforming with SC-FDMA. In a yetalternative embodiment, the transmission scheme may be signaled throughhigher layer (L3) signaling as a user-terminal specific or cell-specificparameter. If the user terminal supports only a fixed transmissionscheme, then no explicit signaling is necessary, and the transmissionscheme is applied according to the capabilities of the user terminal.

FIGS. 5A and 5B illustrate two examples of the distribution of a controlmessage field over the frequency resource. In both FIGS. 5A and 5B, thecontrol message field is distributed (or ‘interleaved’, which is a termcommonly used in this context in OFDM transmission) evenly over thesub-carriers. In other words, control symbols of the control messagefield are mapped to the subcarriers with a frequency-spacing between thecontrol symbols, wherein the spacing is defined by a repetition factorselected for each control message field to define a number of symbolsother than the control symbols of the control message field between thecontrol symbols of the control message field. The frequency-spacingbetween the control symbols of the same control message field may beequal to all control symbols of the control message field in question.FIG. 5A illustrates mapping with a repetition factor two, i.e. thesymbols of the control message field are mapped to every secondsub-carrier. FIG. 5B illustrates mapping with a repetition factor four,i.e. the symbols of the control message field are mapped to every fourthsub-carrier. Different repetition factors may be determined according tothe size of the resource block allocated to the user terminal, sizes ofthe control fields, etc. Naturally, the symbols of the control messagefield are mapped with the repetition factor only to the extent that nomore control symbols exists to map.

The distribution of a given control message field to the allocatedresources may comprise first dimensioning the size of the controlmessage field, then determining the repetition factor and a startingposition sub-carrier index and then mapping symbols of the controlmessage to the corresponding sub-carriers. This is illustrated in FIG. 6illustrating an embodiment of block 404. The flow diagram of FIG. 6illustrates mapping of control message fields to the allocated PUSCHresource. The process of FIG. 6 describes mapping of two control channelfields (CQI and ACK/NACK), but it can easily be expanded to cover othercontrol message fields, as becomes obvious from the description below.In block 502, the number of symbols allocated to each control channelfield (N_(x)) is determined according to the following equation:

$\begin{matrix}{{N_{X} = \left\lceil \frac{{O \cdot {offset} \cdot M_{SC}^{PUSCH}}M_{symb}^{PUSCH}}{K_{bits}^{PUSCH}} \right\rceil},} & (1)\end{matrix}$

where ┌ ┐ denotes rounding operation to the nearest supported integertowards plus infinity, O is the number of bits to be transmitted, e.g.the length of a CQI word, M_(SC) ^(PUSCH) in the allocated is the numberof sub-carriers carrying PUSCH in the allocated frequency resource(received from the base station on physical downlink control channel,PDCCH), M_(symb) ^(PUSCH) is the number of multi-carrier symbols (OFDMsymbols) carrying PUSCH per sub-frame (received from the base station onPDCCH), and K_(bits) ^(PUSCH) is the total number of transmitted bits onthe PUSCH. The term ‘offset’ is a quality offset defining an offsetbetween desired reception qualities of traffic data and control datatransferred in the control message field. The offset may be differentfor different control message fields, but it may also be made dependenton the selected transmission scheme. For example, if the spatialmultiplexing is selected as the transmission scheme, ‘offset’ may be setto have a higher value than in the case of single-stream beamformingtransmission or spatial transmission diversity, where higher reliabilityof transmission is inherently obtained. The quality of the transmissionof traffic data is determined according to the service type of the datatransferred, and the modulation and coding scheme and other parametersof the PUSCH are configured to meet these quality requirements Inpractice, the modulation scheme may be the same for all symbolstransmitted on the PUSCH, as in the current specifications of the LTE-A,but the channel coding scheme of the control message field may beselected on the basis of the ‘offset’. Typically, certain controlmessages, such as ACK/NACK messages, are less tolerant to errors andrequire higher reception quality in terms of block error rate (BLER),for example, and the PUSCH parameters do not automatically meet thesedemands. The term ‘offset’ is used in Equation (1) to ensure that themodulation and coding scheme selected for the control message fieldensures the desired higher reception quality, and the actual value of‘offset’ is determined according to the difference between the quality(BLER) of the traffic data and the required quality (BLER) of thecontrol message type. These values of ‘offset’ are typicallypredetermined and stored as dependent on the selected uplinktransmission scheme. The higher the value of the ‘offset’ is, i.e. thehigher the difference between the required qualities of the traffic dataand the control data, the higher number of symbols is allocated to thecontrol message field and the stronger channel coding is applied to thecontrol message field (and vice versa). Therefore, calculation ofEquation (1) is carried out before modulation and channel coding of thecontrol message bits. As mentioned above, equation (1) is calculated foreach control message type (CQI and ACK/NACK in this example). Equation(1) is actually a modification of an equation defined in current 3GPPspecification, and the modification is the term ‘offset’.

In block 504, a repetition factor RPF is calculated for the CQI messagefield according to the following equation:

$\begin{matrix}{{RPF}_{CQI} = \left\lfloor \frac{N}{N_{CQI}} \right\rfloor} & (2)\end{matrix}$

where N is the total number of subcarriers allocated to the userterminal within a sub-frame and N_(CQI) is the number of CQI symbols tobe transmitted in the sub-frame. └ ┘ denotes floor operation, i.e.rounding to the nearest integer towards minus infinity. The calculationand utilization of the repetition factor ensures that the CQI will bedistributed (or interleaved) over the allocated frequency spectrum.Then, the repetition factor RPF is calculated for ACK/NACK message fieldaccording to the following equation:

$\begin{matrix}{{RPF}_{AN} = \left\lfloor \frac{N - N_{CQI}}{N_{AN}} \right\rfloor} & (3)\end{matrix}$

where N_(AN) is the number of ACK/NACK symbols to be transmitted in thesub-frame. Since the number of CQI resource elements (or symbols) to betransmitted is reduced from the total number of resource elements, therepetition factor RPF_(AN) is calculated by taking into accountlogically available resource elements after the CQI. In this manner,repetition factors for further control message fields (rank indicator,pre-coding matrix indicator, etc) may be calculated by reducing thenumber of allocated resource elements from the total number of resourceelements N before the division by the number of symbols or resourceelements to be used for the particular control message field inquestion. In block 508, different starting position resource elementsare selected for different control message fields so that the resourceelements mapping is started from different resource elements by usingthe allocated repetition factor. The repetition factor may vary between0 and RPF−1. In block 510, control symbols of the control message fieldsare mapped to the resource elements by using the starting positionselected in block 508 and the repetition factor calculated in block 504for CQI and in block 506 for ACK/NACK.

FIG. 6 illustrates the result of the process of FIG. 5, when N=36,N_(CSI)=7, and N_(AN)=4. Accordingly, the repetition factor R_(CQI)becomes 5 (36/7=5.143˜5) according to Equation (2) and R_(AN) becomes 7((36−7)/4=7.25˜7). The starting position of CQI is selected to be 0, andthe starting position of ACK/NACK is selected to be 2 (sub-carrierindices). Now, a CQI symbol is mapped to every fifth sub-carrier,starting from sub-carrier 0, and an ACK/NACK symbol is mapped to everyseventh non-CQI sub-carrier starting from sub-carrier 2. The number ofCQI symbols was excluded in Equation (3), and so they are excluded whencarrying out the actual mapping. After all, it is difficult to findrepetition factors that will never overlap, and the present procedureensures that the ACK/NACK will primarily avoid puncturing a previouslymapped CQI symbol. In case of depletion of data symbols that can bepunctured, ACK/NACK may puncture also CQI symbols, because reliabletransmission of the ACK/NACK message prevails over the transmission ofthe CQI message. In general, no subsequently mapped control messagesymbol will be mapped to the same sub-carrier as a control symbol mappedpreviously, because the mapped resource elements are excluded fromfurther mapping. The mapping may be carried out in the resource elementmapping block 204 of the transmitter, and a similar operation is carriedout in the resource element mapping removal block 222 of the receiver sothat the demapping is carried out correctly.

The actual mapping may be carried out in several ways. The same mappingpattern may be repeated for every OFDM symbol, i.e. the same controlfields may occupy the same sub-carriers from one OFDM symbol to another.The size of a given control message field and the overall size of thecontrol message fields may be made variable from symbol to symbol. Inanother embodiment, a different starting position is selected forconsecutive OFDM symbols so as to obtain a staggered mapping of controlmessage fields in consecutive OFDM symbols. This improves the frequencydiversity between consecutive OFDM symbols, because the control messagefield occupies different frequency positions in different OFDM symbols.Alternatively, the interleaving may be carried out over all thesub-carriers and a plurality of OFDM symbols, e.g. over symbols in thetime slot or sub-frame. Now, when mapping a given control message field,the sub-carrier of the previous OFDM symbol that was mapped last istaken into account when starting mapping the sub-carriers of thesubsequent symbol. For example, if the number of sub-carriers is 36, asin FIG. 6, the sub-carrier index mapped last is 34, and the repetitionfactor is 6, the first sub-carrier mapped in the subsequent OFDM symbolhas index 4. Now, depending on the number of sub-carriers and therepetition factors, different control message fields may occupydifferent sub-carriers in consecutive OFDM symbols.

In a yet alternative embodiment, the interleaving may be carried outover different spatial streams. As mentioned above, it is expected thatuser terminals are equipped with capability to support SU-MIMO, in whichcase multiple spatial transmission streams may be allocated to the userterminal. In such a case, the transmission may be multiplexed into themultiple spatially parallel signal streams. In this case, theinterleaving may be expanded to the multiple streams. The interleavingmay be carried out, for example, by first mapping control symbols to asub-frame of a first stream, then continuing the mapping to the secondstream, and so on. The continuation of the mapping may be carried out ina similar manned to that between consecutive OFDM symbols so that,depending on the number of sub-carriers and the repetition factors,different control message fields may occupy different sub-carriers indifferent spatially parallel streams. Alternatively, the mapping of thesubsequent spatial stream may be initialized to correspond to themapping of the first spatial stream so that the starting position is thesame in both streams. The number of additional symbols available due tothe use of additional signal streams may obviously be taken into accountalso when calculating Equation (1) and the repetition factors. Equation(1) may be modified to accommodate the use of spatial multiplexing, aswill be described later.

In an embodiment, the data symbols may be mapped to the resourceelements before mapping ACK/NACK so that ACK/NACK will puncture datasymbols. In this embodiment, first the interleaving pattern isdetermined for each control message field by calculating Equation (1), arepetition factor, and a starting position for each control messagefield. Then, the CQI and rank indicator symbols are first mapped to theresource elements according to the process of FIG. 5. Thereafter, datasymbols may be mapped to the remaining resource elements. Then, theACK/NACK may be allocated to their determined positions so that anACK/NACK symbol punctures, i.e. takes the place of a data symbol. Thereason for ACK/NACK puncturing data is that, in case the user terminalmisses the reception of a downlink data packet, it is not aware of thepresence of the ACK/NACK message field in the uplink sub-frame and,accordingly, cannot transmit the scheduled ACK/NACK message. Instead, ittransmits data in those resource elements.

In a further embodiment, a determined number of sub-carriers at an edgeof the frequency resource block may be excluded from mapping of controlsymbols. Typically, the sub-carriers at the edge of the frequencyresource are more susceptible to the interference and, therefore,critical control data may be preferably mapped to the sub-carrierscloser to the center frequency of the frequency resource. In practice,this may be carried out by setting the starting position sufficientlyhigh and skipping mapping of the sub-carriers having an index higherthan a determined threshold (the mapping skips to the next symbol). Incase the mapping is continued in the subsequent OFDM symbol from thesub-carrier where the mapping was finished in the previous OFDM symbol,mapping of the sub-carriers having an index lower than another thresholdmay also be skipped.

Utilization of OFDM enables allocation of different transmission powervalues for different resource elements, because the resource elementswill not be spread over the frequency spectrum, as in the SC-FDMA. In anembodiment, different transmission power offset values are assigned tothe resource elements carrying the control message fields and theresource elements carrying the data traffic fields within an OFDMsymbol. A higher transmission power may be assigned to at least somecontrol message fields in the transmitter to ensure their correctreception in the receiver. Naturally different additional transmissionpower offsets may be assigned to different control message fields,depending on how critical signaling information they carry. A highertransmission power may be assigned to more critical control messages.The additional transmission power assigned to the control message fieldsmay also depend on the modulation and coding scheme currently in use onthe PUSCH. The lower the modulation order and the stronger the codingscheme in use, the lower the transmission power offset assigned to thecontrol message fields, because it is considered that theinterference-tolerant modulation and coding scheme compensate for theneed for stronger transmission power.

When utilizing spatial multiplexing as a transmission scheme, theinterleaving pattern may be taken into account in the additional signalstreams, as mentioned above. The control message fields may bedistributed equally to different spatial streams, or the size of controlmessage fields may be defined separately for each spatial stream. Thismay depend on the indication of the CQI from the user terminal. If theuser terminal transmits separate CQIs for each spatial stream, the basestation may define different modulation and coding schemes for differentspatial streams and, therefore, different number of bits may betransmitted in different spatial streams. This is typically enabled whendifferent SU-MIMO spatial streams are coded with different spreading (orscrambling) codes. Otherwise, the same modulation and coding scheme isused for all streams, and an equal amount of control data may beallocated to different spatial streams. This is typically enabled whendifferent SU-MIMO spatial streams are coded with the same spreading (orscrambling) code.

The SU-MIMO uplink transmission may be utilized to improve data rateswith spatial multiplexing or to improve reliability of transmissionthrough beamforming transmission where the transmitted signals aredirected to those spatial channels providing the highest signal-to-noiseproperties. Furthermore, spatial multiplexing can be combined withbeamforming. Another alternative is to use open loop transmit diversitytransmission when essentially the same data is transmitted from allantennas with some pre-coding. As indicated above, the SU-MIMOtransmission may be applied to both OFDM and SC-FDMA transmission, andthe application of Equation (1) and the repetition factors andsub-carrier mapping in case of OFDM transmission has been describedabove. In the case of SC-FDMA transmission, the current SC-FDMA PUSCHstructure illustrated in FIG. 3 may be utilized for all spatial streams.As described in the previous paragraph, the control message fields maybe distributed equally to different spatial streams, or the size of thecontrol message fields may be defined separately for each spatial streamon the basis of the modulation and coding scheme in use. The number ofsymbols to be used for a given control message field is calculated withEquation (1), and the sub-carrier mapping is carried out according tothe pattern illustrated in FIG. 3.

According to an embodiment of the invention, at least part of thecontrol data, e.g. ACK/NACK messages, may be transmitted by usingbeamforming or transmit diversity transmission, while the data trafficmay be transmitted by using the spatial multiplexing. In fact, thismeans that the ACK/NACK is transmitted with the assumption that thechannel rank is one and the data traffic is transmitted with theassumption that the channel rank is higher than one. Equation (1) may bemodified to take into account the spatial multiplexing in a case wheredifferent ranks are determined for a control message type and trafficdata. Equation (1) may be modified by adding an uplink-rank specificparameter ΔR_(D-C) which defines the ratio between the number of ranksof the traffic data and the control message field in question. Forexample, if the rank of the traffic data is two (two spatial streams)and the rank of the ACK/NACK message is one (beamforming or transmitdiversity), ΔR_(D-C) is two (2/1). Equation (1) has the following formafter this modification:

$\begin{matrix}{N_{X} = \left\lceil \frac{{O \cdot {offset} \cdot \Delta}\; {R_{D - C} \cdot M_{SC}^{PUSCH}}M_{symb}^{PUSCH}}{K_{bits}^{PUSCH}} \right\rceil} & (4)\end{matrix}$

Without the modification, the correct number of symbols or sub-carrierswould not be allocated to the control message field because of thedifferent ranks. In order to utilize the beamforming or transmitdiversity for the control message field, the same sub-carriers arepreferably allocated to the control message field in the spatial streamsso that the same control message symbol occupies the same sub-carrier inall spatial streams. Then, a signal processor carrying out thebeamforming in the transmitter multiplies the symbol with a coefficientdetermined on the basis of the desired direction of the beam. A reverseoperation is naturally performed in the receiver to enable reception ofthe symbol, i.e. a signal processor carrying out the beamforming in thereceiver multiplies the signal streams received from multiple antennasby a coefficient determined on the basis of the determined spatialweighting, and the symbols transmitted on the same sub-carriers ofdifferent streams are combined.

FIG. 7 illustrates this embodiment where the ACK/NACK messages aretransmitted from the transmitter to the receiver through a singlespatial transmission stream by using the beamforming technique so as todirect the stream to a desired spatial channel. In other words, the sameACK/NACK message is transmitted from both antenna elements of thetransmitter and the direction is controlled by phase-adjusting thesignals transmitted from the different antennas, as known in the art.Corresponding phase adjustment is performed in the receiver so as toweight the received signals and, thus, amplify the spatial directionfrom which the ACK/NACK is mainly received. The data traffic istransmitted by using spatial multiplexing to achieve higher data rates,and different data is transmitted/received through differenttransmission/reception branches and antennas. In the transmitter and thereceiver, the multi-antenna transmission is controlled by digital signalprocessors 700 and 702 designed for that purpose.

When the uplink transmission scheme is OFDM, the selection betweenbeamforming, transmit diversity, and spatial multiplexing can be made ona sub-carrier level. In such a case, it is preferred that the samesymbols are mapped to the same sub-carriers in each transmission branchin the transmitter, as noted above. When the uplink transmission schemeis SC-FDMA, the selection between beamforming, transmit diversity, andspatial multiplexing may be made on the SC-FDMA symbol level, becauseeach sub-carrier occupies the whole frequency spectrum. The resolutionof the selection between the beamforming, transmit diversity, andspatial multiplexing may be made for each SC-FDMA symbol or for aplurality of SC-FDMA symbols at a time, e.g. for a time slot or asub-frame. If an SC-FDMA symbol carries a control message requiring highreliability, the SC-FDMA symbol may be transmitted by using beamformingor transmit diversity, and the same data is transmitted from all antennabranches in the transmitter and received through all antenna branches inthe receiver. Then, the interleaving pattern determination and mappingof symbols to sub-carriers are made identically for alltransmission/reception branches. On the other hand, if the SC-FDMAsymbol carries information not requiring high reliability, the SC-FDMAsymbol may be transmitted by using spatial multiplexing, i.e. multipleSC-FDMA symbols carrying different information may be transmittedsimultaneously through different spatial streams.

Utilization of the beamforming in transmission of control messagestypically requires feedback information on the channel properties fromthe receiver. When the feedback information is not available, anembodiment of the invention is to transmit at least part of the controlmessage fields by using an open-loop multi-antenna transmit diversityscheme, e.g. space-time block coding, precoding vector switching,frequency-selection transmit diversity, or cyclic delay diversity with alarge or small delay), in order to improve reliability of transmissionof critical control information. The implementation of the open looptransmit diversity schemes listed above is obvious to one skilled in theart, and it does not require substantial modifications to theembodiments described above. The data traffic may be transmitted byusing the spatial multiplexing in order to transmit the data traffic ata higher rate.

As indicated above, the embodiments of the present invention may becarried out in the transmitter (user terminal) and the receiver (basestation). In fact, the embodiments are typically carried out by aprocessor or a corresponding apparatus included in the user terminal orthe base station. The processor is configured to allocate the controlmessage fields to the PUSCH resources according to the selected uplinktransmission scheme so as to optimize transmission performance of thecontrol messages in the selected uplink transmission scheme. Theapparatus may be the processor 700, 702 as illustrated in FIG. 7. Incase no multi-antenna transmission is utilized in the uplinktransmission, the processor 700 of the user terminal simplifies in thesense that it does not carry out multi-antenna signal processing. Theprocessor may be a logical component implemented by multiple physicalsignal processing units. The term ‘processor’ refers to a device that iscapable of processing data. The processor may comprise an electroniccircuit implementing the required functionality, and/or a microprocessorrunning a computer program implementing the required functionality. Whendesigning the implementation, a person skilled in the art will considerthe requirements set for the size and power consumption of theapparatus, the necessary processing capacity, production costs, andproduction volumes, for example. The processor may comprise logiccomponents, standard integrated circuits, microprocessor(s), and/orapplication-specific integrated circuits (ASIC).

The microprocessor implements functions of a central processing unit(CPU) on an integrated circuit. The CPU is a logic machine executing acomputer program, which comprises program instructions. The programinstructions may be coded as a computer program using a programminglanguage, which may be a high-level programming language, such as C,Java, etc., or a low-level programming language, such as a machinelanguage, or an assembler. The CPU may comprise a set of registers, anarithmetic logic unit (ALU), and a control unit. The control unit iscontrolled by a sequence of program instructions transferred to the CPUfrom a program memory. The control unit may contain a number ofmicroinstructions for basic operations. The implementation of themicroinstructions may vary, depending on the CPU design. Themicroprocessor may also have an operating system (a dedicated operatingsystem of an embedded system, or a real-time operating system), whichmay provide the computer program with system services.

The present invention is applicable to the cellular or mobiletelecommunication system defined above but also to other suitabletelecommunication systems. The protocols used, the specifications ofmobile telecommunication systems, their network elements and subscriberterminals develop rapidly. Such development may require extra changes tothe described embodiments. Therefore, all words and expressions shouldbe interpreted broadly and they are intended to illustrate, not torestrict, the embodiment. It will be obvious to a person skilled in theart that, as technology advances, the inventive concept can beimplemented in various ways. The invention and its embodiments are notlimited to the examples described above but may vary within the scope ofthe claims.

1. A method comprising: selecting an uplink transmission scheme for auser terminal of a cellular telecommunication system; determiningphysical uplink shared traffic channel resources of the user terminal;allocating control message fields to the resources of the physicaluplink shared traffic channel according to the selected uplinktransmission scheme so as to optimize transmission performance of thecontrol messages in the selected uplink transmission scheme.
 2. Themethod of claim 1, further comprising: distributing symbols of eachcontrol message over a frequency domain of the physical uplink sharedtraffic channel resources of the user terminal, when the selected uplinktransmission scheme is orthogonal frequency division multiplexing. 3.The method of claim 2, wherein the distribution further comprises:mapping control symbols of each control message field to frequencyresource elements of a symbol block with a frequency-spacing between thecontrol symbols, wherein the spacing is defined by a repetition factorselected for each control message field to define a number of symbolsother than the control symbols of the control message field between thecontrol symbols of the control message field, wherein the symbol blockcarries a plurality of symbols as information elements.
 4. The method ofclaim 3, wherein the distribution further comprises: mapping controlsymbols of each control message to different frequency resource elementsin consecutive symbol blocks in order to achieve frequency diversity. 5.The method according to claim 2, wherein the distribution furthercomprises: distributing the control symbols of each control messagefield evenly over symbol blocks and frequency resource elements of thesymbol blocks available for transmission of the control message.
 6. Themethod of claim 5, wherein the distribution further comprises:distributing the control symbols of each control message evenly oversymbol blocks, frequency resource elements of the symbol blocksavailable for transmission of the control message, and a plurality ofspatial transmission streams when the selected uplink transmissionscheme utilizes spatial multiplexing transmission in uplink.
 7. Themethod according to claim 2, further comprising: assigning differenttransmission power values to the traffic data field and at least onecontrol message field in a symbol block.
 8. The method according toclaim 1, further comprising: determining the number of control symbolsto be allocated to a given control message field in the resources of thephysical uplink shared traffic channel on the basis of the number ofbits to be transmitted in the control message field, the total number ofbits to be transmitted in the resources of the physical uplink sharedtraffic channel, the number of subcarriers in a symbol block, the numberof symbol blocks per sub-frame, and a quality offset defining an offsetbetween desired reception qualities of traffic data and control datatransferred in the control message field; coding the control symbolswith a channel code selected on the basis of the determined number ofcontrol symbols; and mapping the coded control symbols of the controlmessage fields to the frequency resource elements of the symbol blocksaccording to the selected uplink transmission scheme.
 9. The method ofclaim 8, further comprising: determining the number of control symbolsto be allocated to a given control message field in the resources of thephysical uplink shared traffic channel on the basis of the differencebetween multipath channel ranks selected for the control message fieldand the traffic data when the selected uplink transmission schemeutilizes spatial multiplexing transmission in uplink, in order tocompensate for reduction in the size of the control message field whenthe rank of the control message field is lower than the rank of thetraffic data.
 10. The method according to claim 1, further comprising:transmitting at least one control message field by using single-streambeamforming multi-antenna transmission or transmit diversitymulti-antenna transmission and at least data traffic fields by usingmulti-stream spatial multiplexing when the selected uplink transmissionscheme utilizes spatial multiplexing transmission in uplink.
 11. Themethod according to claim 1, further comprising: transmitting at leastone control message field by using open-loop multi-antenna transmissiondiversity and at least data traffic fields by using multi-stream spatialmultiplexing when the selected uplink transmission scheme utilizesspatial multiplexing transmission in uplink.
 12. The method according toclaim 1, further comprising: localizing the control message fields atedges of the physical uplink shared traffic channel resources of theuser terminal when the selected uplink transmission scheme is singlecarrier frequency division multiple access.
 13. The method of claim 12,further comprising: applying the same localization of the controlmessage fields to a plurality of signal branches associated withdifferent antenna elements.
 14. An apparatus comprising a processorconfigured to select an uplink transmission scheme for a user terminalof a cellular telecommunication system, to determine physical uplinkshared traffic channel resources of the user terminal, and to allocatecontrol message fields to the resources of the physical uplink sharedtraffic channel according to the selected uplink transmission scheme soas to optimize transmission performance of the control messages in theselected uplink transmission scheme.
 15. The apparatus of claim 14,wherein the processor is further configured to distribute symbols ofeach control message over a frequency domain of the physical uplinkshared traffic channel resources of the user terminal when the selecteduplink transmission scheme is orthogonal frequency divisionmultiplexing.
 16. The apparatus of claim 15, wherein the processor isfurther configured to map control symbols of each control message fieldto subcarriers of a symbol block with equal frequency-spacing betweenthe control symbols, wherein the spacing is defined by a repetitionfactor selected for each control message field to define a number ofsymbols other than the control symbols of the control message fieldbetween the control symbols of the control message field, wherein thesymbol block carries a plurality of symbols as information elements. 17.The apparatus of claim 16, wherein the processor is further configuredto map control symbols of each control message to different frequencyresource elements in consecutive symbol blocks in order to achievefrequency diversity.
 18. The apparatus according to claim 15, whereinthe processor is further configured to distribute the control symbols ofeach control message field evenly over symbol blocks and frequencyresource elements of the symbol blocks available for transmission of thecontrol message.
 19. The apparatus of claim 18, wherein the processor isfurther configured to distribute the control symbols of each controlmessage evenly over symbol blocks, frequency resource elements of thesymbol blocks available for transmission of the control message, and aplurality of spatial transmission streams when the selected uplinktransmission scheme utilizes spatial multiplexing transmission inuplink.
 20. The apparatus according to claim 15, wherein the processoris further configured to assign different transmission power values tothe traffic data field and at least one control message field in asymbol block.
 21. The apparatus according to claim 14, wherein theprocessor is further configured to determine the number of controlsymbols to be allocated to a given control message field in theresources of the physical uplink shared traffic channel on the basis ofthe number of bits to be transmitted in the control message field, thetotal number of bits to be transmitted in the resources of the physicaluplink shared traffic channel, the number of subcarriers in a symbolblock, the number of symbol blocks per sub-frame, and a quality offsetdefining an offset between desired reception qualities of traffic dataand control data transferred in the control message field; to code thecontrol symbols with a channel code selected on the basis of thedetermined number of control symbols; and to map the control symbols ofthe control message fields to the frequency resource elements of thesymbol blocks according to the selected uplink transmission scheme. 22.The apparatus of claim 21, wherein the processor is further configuredto determine the number of control symbols to be allocated to a givencontrol message field in the resources of the physical uplink sharedtraffic channel on the basis of difference between multipath channelranks selected for the control message field and the traffic data whenthe selected uplink transmission scheme utilizes spatial multiplexingtransmission in uplink, in order to compensate for reduction in the sizeof the control message field when the rank of the control message fieldis lower than the rank of the traffic data.
 23. The apparatus accordingto claim 14, wherein the processor is further configured to transfer atleast one control message field by using single-stream beamformingmulti-antenna transmission or transmit diversity multi-antennatransmission and at least data traffic fields by using multi-streamspatial multiplexing when the selected uplink transmission schemeutilizes spatial multiplexing transmission in uplink.
 24. The apparatusaccording to claim 14, wherein the processor is further configured totransfer at least one control message field by using open-loopmulti-antenna transmission diversity and at least data traffic fields byusing multi-stream spatial multiplexing when the selected uplinktransmission scheme utilizes spatial multiplexing transmission inuplink.
 25. The apparatus according to claim 14, wherein the processoris further configured to localize the control message fields at edges ofthe physical uplink shared traffic channel resources of the userterminal, when the selected uplink transmission scheme is single carrierfrequency division multiple access.
 26. A base station of a cellulartelecommunication system comprising the apparatus according to claim 14.27. A user terminal device of a cellular telecommunication systemcomprising the apparatus according to claim
 14. 28. An apparatuscomprising: means for selecting an uplink transmission scheme for a userterminal of a cellular telecommunication system; means for determiningphysical uplink shared traffic channel resources of the user terminal;and means for allocating control message fields to the resources of thephysical uplink shared traffic channel according to the selected uplinktransmission scheme so as to optimize transmission performance of thecontrol messages in the selected uplink transmission scheme.
 29. Acomputer program product embodied on a distribution medium readable by acomputer and comprising program instructions which, when loaded into anapparatus, execute the method according to claim 1.